Inflatable restraint devices commonly referred to as airbags are used in many applications for motor vehicle occupant impact protection. Airbags are used for frontal impact protection and are generally installed in the vehicle steering wheel for the driver and behind the vehicle instrument panel for other front seat occupants. In addition to frontal impact protection, inflatable restraints are being used in a widespread manner for occupant protection from side impacts. One group of such devices is typically mounted to the vehicle seat or the vehicle body B pillar to protect the lower torso of the occupant. So-called side curtain airbags are typically mounted along the roof rail and deploy in a downward direction to provide an energy absorbing structure between the occupant's upper torso and head, and the vehicle interior components.
Inflatable restraint systems incorporate an inflator which is typically a pyrotechnic device or one using compressed gas (or a hybrid type). A sensor or suite of sensors is provided which cooperate with an onboard controller (electronic control unit or ECU) to sense impact forces and provide a signal to deploy the inflatable restraints. Gas supplied by the inflator quickly inflates the restraint device.
Airbag systems need to be compact when not in use, particularly in view of increasingly stringent packaging requirements associated with modern day passenger car motor vehicles. A particular constrained area is along the roof rail of the vehicle where side curtain airbags are installed. There is little space available in the transverse cross-section of the roof rail between the structural metal components of the roof rail and the interior trim.
Certain designs of side-impact curtain airbag assemblies incorporate an elongated cylindrical inflator which is packaged with a rolled or folded up fabric curtain element with associated bracket elements which are all packaged for mounting to the roof rail. It is desirable to be able to fold and compress the undeployed side curtain to minimize its packaging volume. Further complicating this objective is the presence of gas flow baffles or guides or other internal elements provided to direct inflation gases from the inflator in fore and aft directions, and downward and prevent gases from degrading or rupturing the curtain fabric material. One such flow guide element is referred to as a “Y sock” formed of fabric material and named for the presence of a flow inlet passage and a pair of flow directing ducts. The flow directing elements with the airbag fabric present many layers of material which must be compacted and fit into the tight packaging region available.
A particular design and assembly challenge is posed when mounting the curtain assembly to the vehicle roof rail structure which is normally accomplished using threaded fasteners. Ordinarily a mounting bracket with a pair of mounting flanges or tabs is provided which are oriented to extend downwardly from the compacted side curtain assembly. Fasteners are installed through holes in the mounting tabs. These fasteners typically have an enlarged head or washer provided for structural purposes. An improper assembly which is essential to avoid is a condition where the threaded fastener engages the fabric of the airbag during assembly, pinching it between the fastener head and the mounting tab. This condition could give rise to deployment failures and can structurally compromise the curtain fabric. Various approaches to avoiding these problems have been implemented and proposed. For example, discrete polymer tubs or deflector tabs can be provided which are attached to a sheet metal inflator bracket which protect the area of the mounting tab from interference. It is necessary for these elements to be fastened to the metal bracket before the fastener is installed. While these devices operate satisfactorily in general, the requirement of providing separate components and the intermediate assembly process of fastening these components to the metal bracket adds to cost and complexity of unit assembly. Another solution is to use tape or another restraint wrapping around the assembly to compress the curtain fabric to provide clearance in the fastener area. Unfortunately such approaches may not be satisfactory since is generally not convenient to place such a restraint directly adjacent to the mounting tab where compression of the airbag is needed. Further alternatives may include special assembly aids which push away the side curtain fabric to clear the fastener and drive tool. This approach requires special handling by the assembly operator and verified proper assembly is not readily available. Preferred is a design which inherently prevents the above-mentioned assembly errors from occurring.